Geometric aspects of radiation therapy planning and treatment

ABSTRACT

Radiation treatment planning includes determining a number of beams to be directed into a target, determining directions (e.g., gantry angles) for the beams, and determining an energy level for each of the beams. The number of beams, the directions of the beams, and the energy levels are determined such that the beams do not overlap outside the target and the prescribed dose will be delivered across the entire target.

RELATED U.S. APPLICATION

This application is related to U.S. application Ser. No. 15/657,094, nowU.S. Pat. No. 10,092,774, by R. Vanderstraeten et al., entitled “DoseAspects of Radiation Therapy Planning and Treatment,” filed Jul. 21,2017, and hereby incorporated by reference in its entirety.

BACKGROUND

The use of radiation therapy to treat cancer is well known. Typically,radiation therapy involves directing a beam of high energy proton,photon, ion, or electron radiation (“therapeutic radiation”) into atarget or target volume (e.g., a tumor or lesion).

Before a patient is treated with radiation, a treatment plan specific tothat patient is developed. The plan defines various aspects of thetherapy using simulations and optimizations based on past experiences.In general, the purpose of the treatment plan is to deliver sufficientradiation to the target while minimizing exposure of surrounding normal,healthy tissue to the radiation.

The planner's goal is to find a solution that is optimal with respect tomultiple clinical goals that may be contradictory in the sense that animprovement toward one goal may have a detrimental effect on reachinganother goal. For example, a treatment plan that spares the liver fromreceiving a dose of radiation may result in the stomach receiving toomuch radiation. These types of tradeoffs lead to an iterative process inwhich the planner creates different plans to find the one plan that isbest suited to achieving the desired outcome.

A recent radiobiology study has demonstrated the effectiveness ofdelivering an entire, relatively high therapeutic radiation dose to atarget within a single, short period of time. This type of treatment isreferred to generally herein as FLASH radiation therapy (FLASH RT).Evidence to date suggests that FLASH RT advantageously spares normal,healthy tissue from damage when that tissue is exposed to only a singleirradiation for only a very short period of time. FLASH RT thusintroduces important constraints that are not considered in or achievedwith conventional radiation treatment planning.

SUMMARY

In intensity modulated radiation therapy (IMRT) such as intensitymodulated particle therapy (IMPT), beam intensity is varied across eachtreatment region (target) in a patient. Depending on the treatmentmodality, the degrees of freedom available for intensity modulationinclude beam shaping (collimation), beam weighting (spot scanning), andangle of incidence (which may be referred to as beam geometry). Thesedegrees of freedom lead to effectively an infinite number of potentialtreatment plans, and therefore consistently and efficiently generatingand evaluating high-quality treatment plans is beyond the capability ofa human and relies on the use of a computing system, particularlyconsidering the time constraints associated with the use of radiationtherapy to treat ailments like cancer, as well as the large number ofpatients that are undergoing or need to undergo radiation therapy duringany given time period.

Embodiments according to the present invention provide an improvedmethod of radiation treatment planning, and improved radiation treatmentbased on such planning, for FLASH radiation therapy (FLASH RT). Inembodiments, a prescribed dose to be delivered into and uniformly acrossthe target is determined. Directions (e.g., gantry angles relative tothe patient or target, or nozzle directions relative to the patient ortarget) for delivering beams into the target are determined. This caninclude determining the number of beams (the number of directions fromwhich beams are to be delivered). The directions are determined suchthat the beams do not overlap outside the target; that is, to takeadvantage of the normal tissue sparing effect of FLASH RT, eachsub-volume of normal (healthy) tissue is irradiated only once. The beamscan overlap inside the target. The beams' paths can lie within the sameplane, or they can be in different planes. An energy for each of thebeams is also determined. The number of beams, the directions of thebeams, and beam energies are determined such that the calculated orpredicted cumulative doses inside the target satisfy the prescribed doseacross the target. An iterative process can be used to determine thenumber of beams, the directions of the beams, and beam energies.

In embodiments, a beam energy is determined for each of the directions(for each of the beams). The beam energy for each direction isdetermined such that calculated cumulative doses across the target (atlocations inside the target where the beams' paths overlap) satisfy theprescribed dose. In embodiments, a beam includes a number of beamsegments or beamlets. In one or more such embodiments, a maximum energyfor the beam is specified, and an energy for each of the beam segmentsis determined as a percentage (100 percent or less) or equivalentfraction of the maximum beam energy. In general, beams can have the sameenergy or different energies, and each beam can have a range ofenergies. Thus, different energies can be delivered in differentdirections, and different energies can be delivered in each direction.

Embodiments according to the invention improve radiation treatmentplanning and the treatment itself by expanding FLASH RT to a widervariety of treatment platforms and target sites (e.g., tumors).Treatment plans generated as described herein are superior for sparingnormal tissue from radiation in comparison to conventional techniquesfor FLASH dose rates and even non-FLASH dose rates by reducing, if notminimizing, the magnitude of the dose, and in some cases the integrateddose, to normal tissue (outside the target) by design. When used withFLASH dose rates, management of patient motion is simplified. Treatmentplanning, while still a complex task, is simplified relative toconventional planning.

In summary, embodiments according to this disclosure pertain togenerating and implementing a treatment plan that is the most effective(relative to other plans) and with the least (or most acceptable) sideeffects (e.g., the lowest dose outside of the region being treated).Thus, embodiments according to the invention improve the field ofradiation treatment planning specifically and the field of radiationtherapy in general. Embodiments according to the invention allow moreeffective treatment plans to be generated quickly. Also, embodimentsaccording to the invention help improve the functioning of computersystems because, for example, by reducing the complexity of generatingtreatment plans, fewer computational resources are needed and consumedto develop the plans, meaning also that computer resources are freed upto perform other tasks.

In addition to IMRT and IMPT, embodiments according to the invention canbe used in spatially fractionated radiation therapy including high-dosespatially fractionated grid radiation therapy and microbeam radiationtherapy.

These and other objects and advantages of embodiments according to thepresent invention will be recognized by one skilled in the art afterhaving read the following detailed description, which are illustrated inthe various drawing figures.

This summary is provided to introduce a selection of concepts in asimplified form that is further described below in the detaileddescription that follows. This summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification and in which like numerals depict like elements,illustrate embodiments of the present disclosure and, together with thedetailed description, serve to explain the principles of the disclosure.

FIG. 1 is a block diagram of an example of a computing system upon whichthe embodiments described herein may be implemented.

FIG. 2 is a block diagram illustrating an example of an automatedradiation therapy treatment planning system in embodiments according tothe present invention.

FIG. 3 illustrates a knowledge-based planning system in embodimentsaccording to the present invention.

FIG. 4A is a block diagram showing selected components of a radiationtherapy system upon which embodiments according to the present inventioncan be implemented.

FIG. 4B is a block diagram illustrating a non-coplanar arrangement of agantry and nozzle relative to a patient support device in embodimentsaccording to the invention.

FIG. 4C is a block diagram illustrating a coplanar arrangement of agantry and nozzle relative to a patient support device in embodimentsaccording to the invention.

FIG. 4D is a block diagram illustrating movement of a gantry and nozzlearound a patient support device in embodiments according to theinvention.

FIG. 5 is a flowchart of an example of computer-implemented operationsfor generating a radiation treatment plan in embodiments according tothe present invention.

FIG. 6A illustrates a perspective view of an example of a beam geometryin embodiments according to the invention.

FIG. 6B illustrates a cross-sectional view of an example of a beamgeometry in embodiments according to the invention.

FIG. 6C illustrates a perspective view of an example of a beam geometryin embodiments according to the invention.

FIG. 7A illustrates a beam's eye view of a beam in embodiments accordingto the invention.

FIG. 7B is an example of a depth dose curve for a beam segment inembodiments according to the invention.

FIG. 7C illustrates a cross-sectional view of a target and a beamincluding beam segments in embodiments according to the invention.

FIG. 8 is a flowchart of an example of a computer-implemented radiationtreatment method in embodiments according to the present invention.

FIG. 9 illustrates a method of delivering radiotherapy treatments to inembodiments according to the invention.

FIGS. 10A and 10B illustrate a method of delivering radiotherapytreatments in embodiments according to the invention.

FIG. 11 illustrates a multileaf collimator in embodiments according tothe invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the various embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. While described in conjunction with theseembodiments, it will be understood that they are not intended to limitthe disclosure to these embodiments. On the contrary, the disclosure isintended to cover alternatives, modifications and equivalents, which maybe included within the spirit and scope of the disclosure as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present disclosure, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure.However, it will be understood that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentdisclosure.

Some portions of the detailed descriptions that follow are presented interms of procedures, logic blocks, processing, and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, or the like, isconceived to be a self-consistent sequence of steps or instructionsleading to a desired result. The steps are those utilizing physicalmanipulations of physical quantities. Usually, although not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated in a computing system. It has proven convenient at times,principally for reasons of common usage, to refer to these signals astransactions, bits, values, elements, symbols, characters, samples,pixels, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present disclosure,discussions utilizing terms such as “determining,” “accessing,”“directing,” “controlling,” “defining,” “arranging,” “generating,” orthe like, refer to actions and processes (e.g., the flowcharts of FIGS.5 and 8) of a computing system or similar electronic computing device orprocessor (e.g., the computing system 100 of FIG. 1). The computingsystem or similar electronic computing device manipulates and transformsdata represented as physical (electronic) quantities within thecomputing system memories, registers or other such information storage,transmission or display devices. Terms such as “dose” or “fluence”generally refer to a dose or fluence value; the use of such terms willbe clear from the context of the surrounding discussion.

Portions of the detailed description that follows are presented anddiscussed in terms of a method. Although steps and sequencing thereofare disclosed in figures herein (e.g., FIGS. 5 and 8) describing theoperations of this method, such steps and sequencing are exemplary.Embodiments are well suited to performing various other steps orvariations of the steps recited in the flowchart of the figure herein,and in a sequence other than that depicted and described herein.

Embodiments described herein may be discussed in the general context ofcomputer-executable instructions residing on some form ofcomputer-readable storage medium, such as program modules, executed byone or more computers or other devices. By way of example, and notlimitation, computer-readable storage media may comprise non-transitorycomputer storage media and communication media. Generally, programmodules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. The functionality of the program modules may becombined or distributed as desired in various embodiments.

Computer storage media includes volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules or other data. Computer storage media includes, but isnot limited to, random access memory (RAM), read only memory (ROM),electrically erasable programmable ROM (EEPROM), flash memory or othermemory technology, compact disk ROM (CD-ROM), digital versatile disks(DVDs) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store the desired information and that canaccessed to retrieve that information.

Communication media can embody computer-executable instructions, datastructures, and program modules, and includes any information deliverymedia. By way of example, and not limitation, communication mediaincludes wired media such as a wired network or direct-wired connection,and wireless media such as acoustic, radio frequency (RF), infrared andother wireless media. Combinations of any of the above can also beincluded within the scope of computer-readable media.

FIG. 1 shows a block diagram of an example of a computing system 100upon which the embodiments described herein may be implemented. In itsmost basic configuration, the system 100 includes at least oneprocessing unit 102 and memory 104. This most basic configuration isillustrated in FIG. 1 by dashed line 106. The system 100 may also haveadditional features and/or functionality. For example, the system 100may also include additional storage (removable and/or non-removable)including, but not limited to, magnetic or optical disks or tape. Suchadditional storage is illustrated in FIG. 1 by removable storage 108 andnon-removable storage 120. The system 100 may also containcommunications connection(s) 122 that allow the device to communicatewith other devices, e.g., in a networked environment using logicalconnections to one or more remote computers.

The system 100 also includes input device(s) 124 such as keyboard,mouse, pen, voice input device, touch input device, etc. Outputdevice(s) 126 such as a display device, speakers, printer, etc., arealso included.

In the example of FIG. 1, the memory 104 includes computer-readableinstructions, data structures, program modules, and the like associatedwith an “optimizer” model 150. However, the optimizer model 150 mayinstead reside in any one of the computer storage media used by thesystem 100, or may be distributed over some combination of the computerstorage media, or may be distributed over some combination of networkedcomputers. The functionality of the optimizer model 150 is describedbelow.

FIG. 2 is a block diagram illustrating an example of an automatedradiation therapy treatment planning system 200 in embodiments accordingto the present invention. The system 200 includes an input interface 210to receive patient-specific information (data) 201, a data processingcomponent 220 that implements the optimizer model 150, and an outputinterface 230. The system 200 in whole or in part may be implemented asa software program, hardware logic, or a combination thereof on/usingthe computing system 100 (FIG. 1).

In the example of FIG. 2, the patient-specific information is providedto and processed by the optimizer model 150. The optimizer model 150yields a prediction result. A treatment plan based on the predictionresult can then be generated.

FIG. 3 illustrates a knowledge-based planning system 300 in embodimentsaccording to the present invention. In the example of FIG. 3, the system300 includes a knowledge base 302 and a treatment planning tool set 310.The knowledge base 302 includes patient records 304 (e.g., radiationtreatment plans), treatment types 306, and statistical models 308. Thetreatment planning tool set 310 in the example of FIG. 3 includes acurrent patient record 312, a treatment type 314, a medical imageprocessing module 316, the optimizer model (module) 150, a dosedistribution module 320, and a final radiation treatment plan 322.

The treatment planning tool set 310 searches through the knowledge base302 (through the patient records 304) for prior patient records that aresimilar to the current patient record 312. The statistical models 308can be used to compare the predicted results for the current patientrecord 312 to a statistical patient. Using the current patient record312, a selected treatment type 306, and selected statistical models 308,the tool set 310 generates a radiation treatment plan 322.

More specifically, based on past clinical experience, when a patientpresents with a particular diagnosis, stage, age, weight, sex,co-morbidities, etc., there can be a treatment type that is used mostoften. By selecting the treatment type that the planner has used in thepast for similar patients, a first-step treatment type 314 can bechosen. The medical image processing module 316 provides automaticcontouring and automatic segmentation of two-dimensional cross-sectionalslides (e.g., from computed tomography or magnetic resonance imaging) toform a three-dimensional (3D) image using the medical images in thecurrent patient record 312. Dose distribution maps are calculated by thedose distribution module 320, which may utilize the optimizer model 150.

In embodiments according to the present invention, the optimizer model150 uses a dose prediction model to help shape the dose distribution.The optimizer model 150 can provide, for example, a 3D dosedistribution, fluences, and associated dose-volume histograms for thecurrent patient.

FIG. 4A is a block diagram showing selected components of a radiationtherapy system 400 upon which embodiments according to the presentinvention can be implemented. In the example of FIG. 4A, the system 400includes a beam system 404 and a nozzle 406.

The beam system 404 generates and transports a beam 401 to the nozzle406. In general, the beam 401 can be a proton beam, electron beam,photon beam, ion beam, or atom nuclei beam (e.g., carbon, helium, andlithium). In embodiments, the beam 401 is a proton beam. In anotherembodiment, the beam 401 is an ion beam.

In embodiments, depending on the type of beam, the beam system 404includes components that direct (e.g., bend, steer, or guide) the beamthrough the system in a direction toward and into the nozzle 406. Inembodiments, the radiation therapy system 400 may also include one ormore multileaf collimators (MLCs); each MLC leaf can be independentlymoved back-and-forth by the control system 410 to dynamically shape anaperture through which the beam can pass, to block or not block portionsof the beam and thereby control beam shape and exposure time. The beamsystem 404 may also include components that are used to adjust (e.g.,reduce) the beam energy entering the nozzle 406.

The nozzle 406 may be mounted on or a part of a gantry (FIGS. 4B, 4C,and 4D) that can be moved relative to the patient support device 408,which may also be moveable. In embodiments, the accelerator and beamtransport system 404 is also mounted on or is a part of the gantry. Inanother embodiment, the accelerator and beam transport system isseparate from (but in communication with) the gantry.

The nozzle 406 is used to aim the beam toward various locations (atarget) within an object (e.g., a patient) supported on the patientsupport device 408 in a treatment room. In embodiments, the patientsupport device 408 is a table or couch that supports the patient in asupine position. In another embodiment, the patient support device 408is a chair in which the patient sits. A chair can offer some advantagesrelative to a couch or table. Some patients are uncomfortable in asupine position or find it difficult to stay in that position. A chaircan be moved more easily than a couch. A chair can have more degrees offreedom relative to a couch. In other words, by using a chair, it may bepossible to more comfortably change the position of the patient relativeto the nozzle 406 in more ways than are possible using a couch. As such,use of a chair to move the patient relative to the nozzle 406 may reducethe number of times the heavier gantry needs to be moved or eliminatethe need to move the gantry at all. If the gantry does not need to bemoved, then the nozzle 406 can remain stationary, pointing in a singledirection with the beam directed only towards one wall of the treatmentroom. Consequently, thicker shielding would be needed only for that onewall, reducing costs and also reducing the overall room footprint. Themagnitude of motion for an upright position in a chair is also smallerthan lying down on a couch. This is favorable for high-precisiontreatments. In addition, absolute lung volumes are larger in the uprightposition, which can reduce mean lung dose. A chair also provides largersolid angle coverage, no collisions, and real time tracking.

A target may be an organ, a portion of an organ (e.g., a volume orregion within the organ), a tumor, diseased tissue, or a patientoutline.

The control system 410 of FIG. 4A receives and implements a prescribedtreatment plan. In embodiments, the control system 410 includes acomputer system having a processor, memory, an input device (e.g., akeyboard), and perhaps a display in well-known fashion. The controlsystem 410 can receive data regarding operation of the system 400. Thecontrol system 410 can control parameters of the beam system 404, nozzle406, and patient support device 408, including parameters such as theenergy, intensity, direction, size, and/or shape of the beam, accordingto data it receives and according to the prescribed treatment plan.

As noted above, the beam entering the nozzle 406 has a specified energy.Thus, in embodiments according to the present disclosure, the nozzle 406includes one or more components that affect (e.g., decrease, modulate)the energy of the beam. The term “beam energy adjuster” is used hereinas a general term for a component or components that affect the energyof the particles in the beam, in order to control the range of the beam(e.g., the extent that the beam penetrates into a target), to controlthe dose delivered by the beam, and/or to control the depth dose curveof the beam, depending on the type of beam. For example, for a protonbeam or an ion beam that has a Bragg peak, the beam energy adjuster cancontrol the location of the Bragg peak in the target. In variousembodiments, the beam energy adjuster 407 includes a range modulator, arange shifter, or both a range modulator and a range shifter. That is,when the term “beam energy adjuster” is used, then the element beingdiscussed may be a range modulator, a range shifter, or both a rangemodulator and a range shifter. Examples of a beam energy adjuster forproton beams and ion beams are disclosed in the co-pending patentapplication, U.S. application Ser. No. 15/089,330, now U.S. Pat. No.9,855,445, entitled “Radiation Therapy Systems and Methods forDelivering Doses to a Target Volume”; however, the invention is not solimited.

FIG. 4B is a block diagram illustrating a non-coplanar arrangement of agantry 420 and nozzle 406 relative to a patient support device 408 inembodiments according to the invention. FIG. 4C is a block diagramillustrating a coplanar arrangement of a gantry 420 and nozzle 406relative to a patient support device 408 and also illustrating movementof the gantry and nozzle around the patient support device inembodiments according to the invention. FIG. 4D is a block diagramillustrating movement of the gantry 420 and nozzle 406 around thepatient support device 408 in embodiments according to the invention.This movement can occur in either the non-coplanar arrangement or thecoplanar arrangement.

FIG. 5 is a flowchart 500 of an example of computer-implementedoperations for generating a radiation treatment plan in embodimentsaccording to the present invention. The flowchart 500 can be implementedas computer-executable instructions (e.g., the optimizer model 150 ofFIG. 1) residing on some form of computer-readable storage medium (e.g.,using the computing system 100 of FIG. 1).

In intensity modulated radiation therapy (IMRT) such as intensitymodulated particle therapy (IMPT), beam intensity is varied across eachtreatment region (target) in a patient. Depending on the treatmentmodality, the degrees of freedom available for intensity modulationinclude beam shaping (collimation), beam weighting (spot scanning), andangle of incidence (which may be referred to as beam geometry). Thesedegrees of freedom lead to effectively an infinite number of potentialtreatment plans, and therefore consistently and efficiently generatingand evaluating high-quality treatment plans is beyond the capability ofa human and relies on the use of a computing system, particularlyconsidering the time constraints associated with the use of radiationtherapy to treat ailments like cancer, as well as the large number ofpatients that are undergoing or need to undergo radiation therapy duringany given time period.

In block 502 of FIG. 5, a prescribed dose to be delivered into andacross the target is determined or accessed from a memory of a computingsystem. Each portion of the target can be represented by at least one 3Delement known as a voxel; a portion may include more than one voxel. Aportion of a target or a voxel may also be referred to herein as asub-volume; a sub-volume may include one or more portions or one or morevoxels. As will be described in detail below, each portion or voxel mayreceive radiation from one or more beams delivered from differentdirections. The prescribed dose defines, for example, a dose value, or aminimum dose value and a maximum dose value, for each portion or voxelof the target. In embodiments, the prescribed dose is the same for allportions (sub-volumes or voxels) of the target, such that a uniform doseis prescribed for the entire target.

In block 504, directions (e.g., gantry angles relative to the patient ortarget, or nozzle directions relative to the patient or target) fordelivering beams into the target are determined or accessed from amemory of a computing system. The operation of determining or accessingbeam directions also includes determining or accessing the number ofbeams (the number of directions from which beams are to be delivered).In general, when generating the radiation treatment plan, one goal is todetermine beam paths that minimize the irradiation time of eachsub-volume or voxel of the tissue outside the target. Ideally, eachsub-volume or voxel outside the target is intersected, at most, by onlya single beam. That is, ideally, the beams' paths do not overlap outsidethe target. If some overlap between beam paths is permitted, thenideally each sub-volume or voxel outside the target is intersected bynot more than two beams, with most intersected by only a single beam. Inembodiments, as one means of achieving the aforementioned goal, thedirections are determined such that the total amount of overlap betweenthe beams' paths is minimized outside the target. In another suchembodiment, the directions are determined so that the paths of the beamsdo not overlap at all outside the target. The beams' paths can overlapwithin the target. The beams' paths can lie within the same plane, orthey can be in different planes. Additional information is provided inconjunction with FIGS. 6A, 6B, and 6C.

Any number of other factors may be considered when determining the beamdirections. These factors may include the shape and size (e.g., height Hand width W, or diameter) of the beam in the beam's eye view (see FIG.7A). These factors may also include, for example, the amount or type ofhealthy tissue that a beam will be traveling through. That is, one beamdirection may be more favorable than another if it travels a shorterdistance through healthy tissue or avoids passing through a vital organand may be weighted accordingly.

In block 506 of FIG. 5, a beam energy or intensity is determined foreach of the directions (for each of the beams) or accessed from a memoryof a computing system. The beam energy or intensity for each directionis determined such that the predicted or calculated cumulative doses(e.g., doses calculated using the optimizer model 150 of FIG. 1) atlocations inside the target satisfy the prescribed dose as defined inblock 502. The beam energy or intensity for each direction is determinedsuch that the predicted or calculated cumulative doses (e.g., dosescalculated using the optimizer model 150 of FIG. 1) inside the targetsatisfy the prescribed dose as defined in block 502. In embodiments, abeam includes a number of beam segments or beam lets. In one or moresuch embodiments, a maximum energy (e.g., 80 MeV) for the beam isspecified, and an energy for each of the beam segments is determined asa percentage (100 percent or less) or equivalent fraction of the maximumbeam energy. In general, beams can have the same energy or differentenergies, and each beam can have a range of energies. Thus, differentenergies or intensities can be delivered in different directions, anddifferent energies or intensities can be delivered in each direction.Additional information is provided in conjunction with FIGS. 7A, 7B, and7C.

While the operations in blocks 502, 504, and 506 of FIG. 5 are presentedas occurring in series and in a certain order, the present invention isnot so limited. The operations may be performed in a different orderand/or in parallel, and they may also be performed in an iterativemanner, as the number of beams (and accordingly, the number ofdirections), the beam directions, and the beam energies or intensities(and/or beam segment energies or intensities) used to deliver theprescribed dose are interrelated. The number of beams, their directions,and their energies are determined such the calculated or predicted doseat all the sub-volumes or voxels is the same or within a specifiedtolerance such that a uniform or satisfactorily uniform dose (theprescribed dose) is delivered across the entire target. In particular,in embodiments, the beams are not allowed to overlap outside the target;with this limitation, the number of beams, their directions, and theirenergies are determined such the prescribed dose is delivered across theentire target. As noted above, because of the different parameters thatneed to be considered, the range of values for those parameters, theinterrelationship of those parameters, the need for treatment plans tobe effective yet minimize risk to the patient, and the need to generatehigh-quality treatment plans quickly, the use of the optimizer model 150executing consistently on the computing system 100 (FIG. 1) forradiation treatment planning as disclosed herein is important.

Once a final set of values for number of beams, their directions, andtheir energies are determined, then those values (as well as othervalues for other parameters known in the art) can be stored as aradiation treatment plan in the memory of a computer system, from whichit can be subsequently accessed.

FIG. 6A illustrates a perspective view of an example of a beam geometryin embodiments according to the invention. In the example of FIG. 6A,the beams (exemplified by beam 602) are in the same plane. Each beam candeliver a relatively high dose in a relatively short period of time. Forexample, in embodiments, each beam can deliver doses sufficient forFLASH RT (e.g., at least four (4) grays (Gy) in less than one second,and as much as 20 Gy or 50 Gy or more in less than one second). Inembodiments, the range is 0.01-500 Gy. As described herein, each beamcan include one or more beam segments or beam lets. In this example, thebeams' paths overlap only within the target 604, and do not overlapoutside the target in the surrounding tissue 606.

Although multiple beams are shown in FIG. 6A, this does not mean thatall beams are necessarily delivered at the same time or in overlappingtime periods, although they can be. The number of beams delivered at anyone time depends on the number of gantries or nozzles in the radiationtreatment system (e.g., the radiation treatment system 400 of FIG. 4A)and on the treatment plan.

FIG. 6B illustrates a cross-sectional view of an example of a beamgeometry in embodiments according to the invention. In this example, thebeams (exemplified by beams 605 and 607) overlap only within the targetand are in the same plane. The figure depicts the beams in overlappingfashion to demonstrate that each portion of the target 604 receives adose of radiation.

In the examples of FIGS. 6A and 6B, the beams are illustrated as notextending beyond the distal edge of the target 604 (as could be the casefor a proton beam or an ion beam); however, the invention is not solimited. Each beam can deliver a relatively high dose in a relativelyshort period of time. For example, each beam can deliver dosessufficient for FLASH RT.

As will be discussed further in conjunction with FIG. 7C, forimplementations in which the beams have a Bragg peak, such as a protonbeam or an ion beam, the dose delivered by a beam (or beam segment) isnot necessarily uniform along the entire length of the beam path throughthe target 604. Thus, for example, for a proton or ion beam, the dosedelivered by the beam 605 at the proximal portion (or edge) 608 of thetarget 604 may be different from (e.g., less than) the dose delivered bythat beam at the distal portion (or edge) 610 of the target (here,proximal and distal are with reference to the source of the beam 605).The same can be said for each proton or ion beam.

The dose delivered to each portion of the target 604 is cumulative,based on the number of beams that are delivered to and through thatportion. For example, the portions of the target 604 covered by thebeams 605 and 607 receive a total dose that is the sum of the dosedelivered by the beam 605 and the dose delivered by the beam 607. Inembodiments, the energies of the beams (beam segments) are accuratelydetermined so that, even though the dose along each beam (or beamsegment) is not uniform, a uniform cumulative dose distribution isachieved within and across the target 604.

FIG. 6C illustrates a perspective view of an example of a beam geometryin embodiments according to the invention. In the example of FIG. 6C,the beams (exemplified by beam 612) are in different planes. Asdescribed herein, each beam can include one or more beam segments orbeam lets. In this example, the beams' paths overlap only within thetarget 604, and do not overlap outside the target in the surroundingtissue 606. Although multiple beams are shown in the figure, all beamsare not necessarily delivered at the same time or in overlapping timeperiods as mentioned above. Each beam can deliver a relatively high dosein a relatively short period of time. For example, each beam can deliverdoses sufficient for FLASH RT.

For implementations that use proton beams or ion beams, the dosedelivered by each beam at the respective proximal portion (or edge) ofthe target 604 may be different from (e.g., less than) the dosedelivered by that beam at the respective distal portion (or edge) of thetarget (as before, proximal and distal are with reference to the sourceof the beam).

The dose delivered to each portion of the target 604 is cumulative,based on the number of beams that are delivered to and through thatportion. Not all beams are depicted in the figures for simplicity; ingeneral, the number of beams is sufficient to achieve a uniformcumulative dose distribution within the target 604.

In general, the surface of a target can be viewed as having a number ofdiscrete facets. From this perspective, for beams other than photonbeams, each incident beam is orthogonal to each facet such that thebeams do not overlap outside the target. In the case of photon beams,each incident beam is parallel to the facet and does not overlap otherbeams outside the target.

FIG. 7A illustrates a beam's eye view (BEV) of a beam 702 in embodimentsaccording to the invention. That is, FIG. 7A illustrates a cross-sectionof a beam. The beams of FIGS. 6A, 6B, and 6C are examples of the beam702. The beam 702 is illustrated as being rectangular in shape having aheight H and width W. However, the invention is not so limited, and thebeam 702 can have virtually any regular or irregular cross-sectional(e.g., BEV) shape. For example, the shape of the beam 702 can be definedusing an MLC that blocks a portion or portions of the beam. Differentbeams can have different shapes.

In the FIG. 7A embodiment, the beam 702 includes a number of beamsegments or beam lets (that also may be referred to as spots)exemplified by beam segments 704, 706, and 708. A maximum energy (e.g.,80 MeV) is specified for the beam 702, and an energy level is definedfor each of the beam segments as a percentage or fraction of the maximumenergy. By weighting the energy per beam segment, in effect theintensity of each beam segment is also weighted. The energy per beamsegment is defined so that the beam segment will deliver a fraction ofthe prescribed dose such that, in combination with the other beamsegments in the beam, and in combination with the other beams (and beamsegments), a uniform (homogeneous) cumulative dose that satisfies theprescribed dose will be delivered within and across the volume of thetarget. The defined energy level or intensity can be realized for eachbeam segment using the beam energy adjuster 407 of FIG. 4A.

Each beam segment can deliver a relatively high dose in a relativelyshort period of time. For example, each beam segment can deliver atleast 4 Gy in less than one second, and may deliver as much as 20 Gy or50 Gy or more in less than one second. The energy or intensity of eachbeam segment can be controlled using the beam energy adjuster 407 ofFIG. 4A so that the beam segment has sufficient energy to reach thedistal edge of the target.

In operation, in embodiments, the beam segments are deliveredsequentially. For example, the beam segment 704 is delivered to thetarget (turned on) and then turned off, then the beam segment 706 isturned on then off, then the beam segment 708 is turned on then off, andso on. Each beam segment may be turned on for only a fraction of asecond (on the order of milliseconds).

FIG. 7B is an example of a depth dose curve for a beam segment for abeam such as a proton beam or an ion beam that has a Bragg peak inembodiments according to the invention. The example of FIG. 7B showscalculated dose level as a function of depth in the target (distancefrom the beam source). The energy level or intensity of each beamsegment can be controlled using the beam energy adjuster 407 (FIG. 4A)such that the Bragg peak is in the portion at (adjacent to or near) thedistal edge of the target as shown in FIG. 7B.

With reference back to FIG. 6B, it can be seen (or deduced) that greaterportions of each beam overlap toward the center of the target 604 thanat the edges of the target, and more beams overlap at or near the centerof the target 604 than at the edges of the target. For example, thebeams 602 and 603 do not overlap at the proximal edge 608 of the target604, overlap more toward the center of the target, overlap completely ator near the center of the target, and overlap partially past the centerand at the distal edge 610. All beams overlap at the center of thetarget 604, but all beams do not overlap at the edges of the target. Asmentioned previously herein, the dose contributed by each beam iscumulative, and the target 604 can be represented by the 3D elementsknown as voxels or sub-volumes. Each voxel or sub-volume will receiveradiation from one or more beam segments delivered from differentdirections. The total dose for a voxel/sub-volume is the sum of thedoses delivered by each beam segment received by the voxel. By shapingthe beam segments as shown in the example of FIG. 7B for beams (e.g.,proton beams and ion beams) that have a Bragg peak, the portions orvoxels or sub-volumes in the target 604 that are traversed by fewerbeams (beam segments) will receive a larger dose per beam segmentbecause the Bragg peaks of those beam segments coincide with thelocations of those portions/voxels/sub-volumes, while theportions/voxels/sub-volumes in the target that are traversed by morebeams (beam segments) will receive a smaller dose per beam segmentbecause the Bragg peaks of the latter beam segments do not coincide withthe locations of the latter portions/voxels. In other words, the Braggpeak of each beam is at the distal edge of the target 604, where thereis less overlap between beams, and the dose per beam is less than theBragg peak at locations inside the target where there is more overlapbetween beams. In this manner, for embodiments that use beams that haveBragg peaks, a uniform dose can be delivered within and across thetarget 604.

FIG. 7C illustrates a cross-sectional view of an irregularly shapedtarget 715 and a beam 720 that includes four beam segments 721, 722,723, and 724 in the longitudinal direction in embodiments according tothe invention. As described above, the energy of each of the beamsegments 721, 722, 723, and 724 can be individually defined andindependently controlled (e.g., using the beam energy adjuster 407 ofFIG. 4A) so that the beam segment has sufficient energy to reach thedistal edge of the target 715. In particular, for beams like protonbeams and ion beams that have Bragg peaks, the energy level of the beamsegments 721, 722, 723, and 724 can be independently controlled usingthe beam energy adjuster 407 such that the Bragg peak of each beamsegment is in the portion at (adjacent to or near) the distal edge ofthe target 715. In this manner, the range of the beam 720 can be shapedso that it follows the shape of the target 715 in the longitudinaldirection. The cross-sectional size (e.g., height and width or diameter)of each beam segment can be specified according to the complexity of theshape of the target 715. For example, if the target surface isrelatively uniform (e.g., flat), then the size of the beam segment canbe larger.

FIG. 8 is a flowchart 800 of an example of a computer-implementedradiation treatment method in embodiments according to the presentinvention. The flowchart 800 can be implemented as computer-executableinstructions residing on some form of computer-readable storage medium(e.g., using the control system 410 of FIG. 4).

In block 802 of FIG. 8, a radiation treatment plan is accessed. Theradiation treatment plan includes a prescribed dose to be delivereduniformly across a target, a number of beams, directions of the beams,and beam energies for the beams, where the number of beams, thedirections of the beams, and the beam energy for each of the beams aredetermined such that calculated cumulative doses at sub-volumes insidethe target satisfy the prescribed dose. Such a radiation treatment plancan be generated using the methodology described in conjunction withFIG. 5.

In block 804, the beams are directed into the target according to thetreatment plan, thereby delivering the prescribed dose uniformly acrossthe target.

FIG. 9 illustrates a method of delivering photon FLASH radiotherapytreatments to both a target (e.g., a tumor) and normal (healthy) tissueoutside the target using a rapidly rotating (e.g., slip ring) gantry inembodiments according to the invention. In these embodiments, treatmentis performed on a slice-by-slice or small volume-by-small volume basisusing a type of IMRT such as volumetric modulated arc therapy (VMAT) ortomotherapy. In FIG. 9, three organs-at-risk (OAR1, OAR2, and OAR3) anda planning target volume (PTV; e.g., a tumor) are shown. As illustrated,OAR1 is irradiated twice at point 902 when the source is at twodifferent gantry positions (A and D), thus leading to a finite Ti (thetime between different irradiations to a single sub-volume). Thisimplies that Ti is to be taken into consideration in treatment planning.The advantage of treating on a slice-by-slice basis is that MLC leafspeed requirements are reduced because MLC leaf travel lengths per unittime are reduced. In embodiments, to maintain the FLASH effect, movementof the gantry is controlled so it does not traverse more 180 degreesbefore advancing to the next slice in order to avoid opposing beamsirradiating the same volume. Treatment may be delivered using modes suchas continuous table motion or by step-and-shoot (SS). In both modes,care is taken to ensure that the transition regions between slices arestill FLASH-type because some sub-volumes in the transition region couldbe (partly) irradiated from two different slice positions.

In the present embodiments, system requirements are illustrated by thefollowing example. To deliver 20 Gy at a rate of 40 Gy/sec, the gantryshould rotate though 180 degrees in less than 0.5 seconds (60 RPM).Assuming a five millimeter slice and an MLC modulation factor of three,required gantry and MLC leaf speeds on can be achieved usingconventional radiotherapy devices. Technologies relevant to high speedMLCs include pneumatic or electromagnetic drives.

FIGS. 10A and 10B illustrate a method of delivering photon FLASHradiotherapy treatments using fixed gantry angles in embodimentsaccording to the invention. In these embodiments, FLASH criteria areonly maintained for normal tissue. In the FIG. 10 example, three fixedfields (A, B, and C) are shown in FIG. 10A. The MLC leaves can progressthrough the axial volume on a slice-by-slice base to minimize leaftravel distances and to minimize Ti. Treatment plans are accordinglydevised so that a given volume of normal tissue is irradiated onlythrough a minimal number of gantry angles to further minimize Ti.However, the PTV (e.g., tumor) may be irradiated from multiple gantryangles because, in some of the present embodiments, the FLASH criteriaare not intended to be maintained.

Compared to the FIG. 9 embodiments, gantry rotation and MLC leaf speedrequirements can be relaxed provided that the treatment plan isconstrained so that a given volume of normal tissue is only irradiatedfrom nearby gantry angles, thus minimizing Ti. In embodiments, the MLCshould be able to move rapidly over a short distance equal to the slicethickness; this can be achieved using an MLC (e.g., a binary MLC) thatemploys pneumatic drives.

FIG. 11 illustrates a quantized, multilayer MLC 1100 in embodimentsaccording to the invention. In embodiments, each layer is only partiallyattenuating. In addition, in embodiments, the entire assembly is able tomove in the axial (z) direction to cover multiple slices without havingto move the patient. The motion in the axial direction need not be asfast as the rapid motion of the individual leaves. Also, it is notnecessary to have both halves of the MLC assembly if leaf motion issufficiently fast (e.g., either the leaves 1102 or the leaves 1104 canbe replaced with a stationary or solid blocker).

In the embodiments of FIGS. 9, 10, and 11, delivered dose rates above 25Gy/sec are achievable. In embodiments, Ti (the length of the timeintervals separating different irradiations of the same sub-volume) canbe advantageously reduced or minimized. For example, to deliver a totalof four Gy in a single beam increment at a rate of 40 Gy/sec, the amountof time required is 0.1 seconds. In comparison, to maintain the doserate criterion and deliver four Gy in two equal beam increments of twoGy each, each beam increment would be delivered in 0.05 seconds at arate of 40 Gy/sec. It is desirable to reduce or minimize Ti (the timebetween the two increments) to satisfy the criterion of delivering alarge dose in a short time and still be able to take advantage of thenormal tissue sparing effect of FLASH RT. In effect, in this example, ifthe two beam increments pass through the same sub-volume of normaltissue, then that sub-volume may be considered to have been irradiatedonly once if Ti is short enough.

In summary, embodiments according to the invention improve radiationtreatment planning and the treatment itself by expanding FLASH RT to awider variety of treatment platforms and target sites. Treatment plansgenerated as described herein are superior for sparing normal tissuefrom radiation in comparison to conventional techniques even fornon-FLASH dose rates by reducing, if not minimizing, the magnitude (andthe integral in some cases) of the dose to normal tissue (outside thetarget) by design. When used with FLASH dose rates, management ofpatient motion is simplified. Treatment planning, while still a complextask of finding a balance between competing and related parameters, issimplified relative to conventional planning. The techniques describedherein may be useful for stereotactic radiosurgery as well asstereotactic body radiotherapy with single or multiple metastases.

In addition to IMRT and IMPT, embodiments according to the invention canbe used in spatially fractionated radiation therapy including high-dosespatially fractionated grid radiation therapy and microbeam radiationtherapy.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A computing system comprising: a centralprocessing unit (CPU); and memory coupled to the CPU and having storedtherein instructions that, when executed by the computing system, causethe computing system to execute operations to generate a radiationtreatment plan, the operations comprising: accessing a minimumprescribed dose to be delivered into and across a target; determining anumber of beams and directions of the beams, wherein the directions aredetermined such that the beams do not overlap outside the target, andwherein each beam of the beams comprises a plurality of beam segments;determining a maximum beam energy for said each beam; and for said eachbeam, determining a beam segment energy for each beam segment of theplurality of beam segments as a percentage of the maximum beam energy,wherein the number of the beams, the directions of the beams, and themaximum beam energy for said each beam are determined such that theentire target receives the minimum prescribed dose.
 2. The computingsystem of claim 1, wherein the beams overlap inside the target.
 3. Thecomputing system of claim 1, wherein the beams comprise beams havingpaths that are in a same plane.
 4. The computing system of claim 1,wherein the beams comprise beams having paths that are in differentplanes.
 5. The computing system of claim 1, wherein the beams areselected from the group consisting of proton beams and ion beams andhave a respective Bragg peak associated therewith, wherein saki eachbeam segment is controlled to position its respective Bragg peak in aportion of the target at a distal edge of the target.
 6. The computingsystem of claim 1, wherein the number of the beams, the directions ofthe beams, and the maximum beam energy for said each beam are determinedusing an iterative process, wherein the operations further compriseadjusting the number of the beams, the directions of the beams, and themaximum beam energy for said each beam in the iterative process.
 7. Anon-transitory computer-readable storage medium havingcomputer-executable instructions for causing a computing system toperform a method of radiation treatment planning, the method comprising:accessing information specifying a prescribed dose to be delivered intoand throughout a target; determining a number of beams to be directedinto the target; determining gantry angles for directing the beams intothe target; and determining a beam energy for each of the beams, whereinthe number of beams, the gantry angles, and the beam energy for each ofthe beams are determined such that the beams do not overlap outside thetarget and calculated cumulative doses at all sub-volumes inside thetarget satisfy the prescribed dose; wherein said each of the beamscomprises a respective plurality of beam segments, wherein the methodfurther comprises: determining a respective maximum beam energy for saideach of the beams; and determining a beam energy for each beam segmentof each of the respective plurality of beam segments as a percentage ofthe respective maximum beam energy.
 8. The non-transitorycomputer-readable storage medium of claim 7, wherein the gantry anglesare determined such that the beams overlap inside the target.
 9. Thenon-transitory computer-readable storage medium of claim 7, wherein thegantry angles are determined such that the beams are in a same plane.10. The non-transitory computer-readable storage medium of claim 7,wherein the gantry angles are determined such that the beams are indifferent planes.
 11. The non-transitory computer-readable storagemedium of claim 7, wherein the beams are selected from the groupconsisting of proton beams and ion beams and have a respective Braggpeak associated therewith, wherein said each beam segment of said eachof the respective plurality of beam segments is controlled to positionits respective Bragg peak in a portion of the target at a distal edge ofthe target.
 12. A radiation treatment method, comprising: accessing aprescribed dose to be delivered uniformly across a target; determining anumber of beams and directions of the beams, wherein the directions aredetermined such that the beams do not overlap outside the target, andwherein each beam of the beams comprises a plurality of beam segments;determining a maximum beam energy for said each beam; determining a beamsegment energy for each beam segment of the plurality of beam segmentsas a percentage of the maximum beam energy, wherein the number of thebeams, the directions of the beams, and the maximum beam energy for saideach beam are determined such that the entire target receives theprescribed dose, and wherein the number of the beams, the directions ofthe beams, the maximum beam energy for said each beam, and the beamsegment energy for said each beam segment comprise elements of aradiation treatment plan; and directing the beams into the targetaccording to the radiation treatment plan.
 13. The method of claim 12,wherein the beams overlap inside the target.
 14. The method of claim 12,wherein paths of the beams are in a same plane.
 15. The method of claim12, wherein paths of the beams are in different planes.
 16. The methodof claim 12, wherein the beams are selected from the group consisting ofproton beams and ion beams and have a respective Bragg peak associatedtherewith, wherein each beam segment is controlled to position itsrespective Bragg peak in a portion of the target at a distal edge of thetarget.